Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1612909

Description of problem:
Concurrent creation of subnets can lead to records with duplicate names

Version-Release number of selected component (if applicable):
Verified in 6.3, as well as in upstream, has been around probably from the beginning

How reproducible:
Under concurrent requets

for x in {1..20}; do
echo "Attempt $x"
for y in {1..4}; do
curl k -u admin:changeme -X POST -d '{"name":"subnet'$x'","network":"192.168.0.1","mask":"255.255.255.0"}' -H 'Content-Type: application/json' http://localhost:300/api/v2/subnets &
done
sleep 1
done

Actual results:

select name, count() from subnets group by name having count() > 1;

returns multiple records

Expected results:

select name, count() from subnets group by name having count() > 1;

returns no record.

Additional info:

Testing notes: when verifying, please first generate multiple subnets with an installation without this fix and try to migrate to the version with it.